Former pope exploded while on display after embalming went horribly wrong

67 years ago, the reign of Pope Pius XII ended in a horrific manner all thanks to an embalming process that that went very, very wrong.

Officially declared 'venerable' by the late Pope Benedict XVI for his spiritual perfection and wisdom, Pope Pius XII - born Eugenio Maria Giuseppe Giovanni Pacelli - operated as the Bishop of Rome for almost two decades until his death via acute heart failure in October 1958.

However, by breaking tradition on the physician's table, he inadvertently carved himself into the annals of history for a rather gruesome reason too.

There's no other way to put this: Pius XII's body gradually exploded over the course of his four-day ceremonial viewing event.

When you reach such heights in the Roman Catholic Church, millions of acolytes enter an elaborate mourning process when you die, which we've all been reminded of this week following the recent death of Pope Francis, aged 88.

Pope Pius XII reigned for 19 years in total (Bettmann / Contributor via Getty)

For the last few days, Francis' body has been on display in an open casket at St Peter's Basilica, before he'll be buried 'without particular decoration' after the funeral this weekend.

One thing Pope Francis didn't request prior to his death - unlike Pius XII - was for his organs to remain unpreserved inside his corpse, which brings us back to the exploding pope of the '50s.

Typically, the individual responsible for preserving the holy body would drain all of its tissues and internal organs before filling it with preservation fluid. Complete removal of the organs, à la the Ancient Egyptians, is even better, but Pius XII had tasked physician Riccardo Galeazzi-Lisi with jettisoning those conventions, IFLScience reports.

Galeazzi-Lisi proceeded to soak the body with oils before wrapping it in plastic layers, yet the country's seasonal hot weather produced the perfect conditions for Pius XII's internal bacteria to thrive, quickening decomposition, and so a gassy disaster was inevitable.

Pope Francis passed away on Easter Monday this year (Vatican Media via Vatican Pool/Getty Images)

Recounting what went down, Professor Ken Donaldson at The Anatomy Lab, Surgeons Hall Museums, shared: "Although it was in line with Pius's wishes to be buried ‘as God had made him’, you may spot the mistake in that the internal organs were not preserved in this approach.

"Inevitably autolysis, plus putrefaction caused by the gut bacteria, were soon generating large amounts of gas inside the body.

"Over the 4-day course of the viewing and funeral ceremony, the Pope’s chest ‘exploded’ due to build-up of gas in the chest cavity, then the nose and fingers fell off and the body turned a greenish black colour."

He added: "The smell was so sickening that some guards fainted, and guarding could only be made bearable by changing the guard every 15 minutes."